Optic nerve damage as the central mechanism
The defining feature of glaucoma is progressive damage to the optic nerve. This damage interferes with the transmission of visual signals to the brain and leads to gradual changes in vision.
The optic nerve is composed of millions of nerve fibres, and in glaucoma these fibres are progressively lost. Because these fibres do not regenerate, any damage that occurs is permanent.
The role of intraocular pressure
Intraocular pressure (IOP) is one of the most important factors associated with the development of glaucoma. It is determined by the balance between the production and drainage of aqueous humour within the eye.
When this balance is disrupted, pressure may increase. Elevated pressure can place mechanical stress on the optic nerve, contributing to damage over time.
However, glaucoma can also occur in individuals with normal pressure levels, indicating that pressure alone does not fully explain the condition.
Aqueous humour dynamics
Aqueous humour is continuously produced inside the eye and must drain efficiently to maintain stable pressure. It flows through the anterior chamber and exits via a specialised drainage system.
If drainage becomes less efficient, fluid accumulates and pressure may rise. In some cases, the drainage system remains anatomically open but functions less effectively, leading to gradual pressure elevation.
In other situations, structural narrowing or blockage of the drainage pathway can restrict fluid outflow more significantly.
Shows how fluid is created by the ciliary body, then travels through the pupil, and exits via the trabecular meshwork, and how critical this circulation is to keeping the eye inflated, nourished, and healthy..Mechanical stress on the optic nerve
Elevated intraocular pressure can create mechanical strain on the optic nerve head, particularly at the point where nerve fibres exit the eye.
This area, known as the lamina cribrosa, is especially vulnerable to pressure-related changes. Increased stress in this region can disrupt nerve fibre function and contribute to progressive damage.
Vascular factors and blood supply
The optic nerve depends on a stable blood supply to maintain its function. Reduced or fluctuating blood flow can make the nerve more vulnerable to damage.
In some forms of glaucoma, particularly those occurring at normal pressure levels, vascular factors are thought to play a significant role. Changes in blood flow regulation may affect how well the optic nerve is supported.
Structural characteristics of the eye
Individual anatomical differences can influence how glaucoma develops. The structure of the optic nerve, the thickness of the cornea and the configuration of the drainage angle all play a role in how the eye responds to pressure and stress.
These variations help explain why some individuals develop optic nerve damage under conditions that do not affect others.
Susceptibility of the optic nerve
Not all optic nerves respond to stress in the same way. Some are more resilient, while others are more susceptible to damage from pressure or reduced blood supply.
This variability means that similar pressure levels may have very different effects in different individuals.
Secondary mechanisms
In some cases, optic nerve damage develops as a result of other processes within the eye. These may include inflammatory changes, structural alterations or disruptions to normal fluid dynamics.
The underlying mechanism can vary depending on the specific form and context in which the condition develops.
Multifactorial nature of the condition
Glaucoma is not caused by a single factor, but rather by the interaction of multiple mechanisms. Mechanical stress, vascular factors and structural characteristics all contribute to optic nerve damage.
Understanding this multifactorial nature is important in guiding assessment and long-term management.